California and Idaho are both members of the Drivers License Compact. This DLC requires member states to report tickets received by motorist to the state where they received a license to drive. So the Idaho courts or Transportation Department will notify the California Department of Vehicles about this out of state speeding ticket.

Typically if you ignore or do not take care of a speeding ticket from a state in which your state has a reciprocal agreement, like CA and ID have, you license will be suspended in the state in which you received the ticket. Your home state, California, will then likely be informed that you failed to pay or otherwise take care of your speeding violation.

California at that time might extend the Idaho suspension to your CA license or take other action. If the offense had occurred in California and you failed to pay a traffic violation, the DMV would check when it is time to renew the registration on your vehicle to see if there are any outstanding issues. If a failure to pay or appear is found, the DMV can refuse to renew your vehicle registration

To find out for certain what California does with regards to your license and driving record if you do not take care of out of state tickets you can contact the CA DMV.